The present invention relates generally to a controller for AC motors. More particularly, the invention relates to a motor controller having a compact construction that can be easily coupled between a source of AC power and a motor via readily accessible input and output terminals anchored to a control circuit board within the controller.
In recent years the popularity of AC motor controllers, particularly variable frequency motor controllers, has grown tremendously. Such controllers find application in virtually all facets of industry, including material handling, manufacturing and process control. Also referred to as motor drive packages, these controllers are designed for installation between a source of AC power and the motor to be controlled and offer the engineer considerable flexibility in adapting the drive characteristics of the controller to the particular application on which the motor is installed. Once practical only on applications involving large motors using complex hard-wired relay circuits, sophisticated motor controllers are now commonly available for small AC motors as well. Moreover, the use of solid state programmable circuitry has permitted even small motor controllers to offer even greater flexibility in a compact and economical package.
Known AC motor controllers of this type, particularly controllers for smaller horsepower motors (e.g. 5 horsepower and below), generally include a number of solid state power components, such as rectifying circuitry and inverting circuitry, typically including insulated gate bipolar transistors (IGBT's), as well as lower voltage isolation, drive and monitoring circuits for driving the IGBT's and for monitoring certain operating parameters of the drive. In addition, such controllers include a logic circuit board supporting components such as a microprocessor, and a power supply board supporting circuitry for supplying power to the switching devices and logic circuitry. While the lower voltage logic circuitry is thus typically separated from the higher voltage components, it is common in the art to support both the input rectifying circuitry, the IGBT circuitry and the isolation, drive and monitoring circuitry on a single drive circuit board.
In operation, the controller is wired to input phase conductors and the rectifying circuit converts incoming AC power to DC power. The DC power is transmitted to the inverting circuit via a DC bus. The inverting circuit reconverts the DC power to AC power at controlled voltage, current and frequency in response to control signals generated by the logic control circuitry in accordance with preset control routines. The controlled AC power is then transmitted to the motor via output conductors to drive the motor.
In addition to the various components and circuitry, known motor controllers typically include a single input and output terminal strip for connection to incoming AC power conductors, to the motor being driven and to any external circuit components such as braking resistors and the like. The terminal strip is typically supported on the same drive circuit board as the power circuitry and incoming power is transmitted from the controller input terminals to the input rectifying circuit via conductor paths on the circuit board. Moreover, outgoing, controlled waveform AC power is transmitted from the inverting circuitry to the output terminals via similar conductor paths.
Several disadvantages are associated with this conventional configuration. First, the conductor paths used to route power to and from the power circuitry can lead to significant heating due to ohmic power losses. Moreover, routing the conductor paths and mounting the terminal strip on the drive circuit board substantially increases the footprint of the drive circuit board and, consequently, the physical size of the drive. Furthermore, because in the assembled drive package the drive circuit board is housed within an enclosure, such as a plastic cover, installation and servicing of the drive requires that the cover be repeatedly removed and replaced for access to the terminal strip. Finally, manipulation of the connectors on the terminal strip can cause movement of the drive circuit board, resulting in weakening or breaking connections between the board and other system components.